setUp and tearDown

Learn fixtures with setUp and tearDown.

setUp and tearDown

setUp(() { ... }) runs before each test, tearDown(() { ... }) runs after each test. This prepares a clean environment (fixture) for each test.

For example a Counter instance created in setUp lets every test start fresh. tearDown closes temporary files or connections.

These methods can be used inside a group; they then run only for that group's tests.

The fixture concept

A fixture is the environment a test runs in. In setUp you create an object and place it in a variable shared by tests. Each test receives it fresh.

For example late Counter c; setUp(() { c = Counter(); }); produces a new Counter for each test. Tests no longer affect each other.

tearDown cleans up at the end; it deletes temp files or closes connections.

Exercise The Counter class

Define a Counter class with an int value = 0 field and a void increment() => value++ method. In main create a Counter, call increment() three times and print value with print.

Show example solution

class Counter {
  int value = 0;
  void increment() => value++;
}

void main() {
  var c = Counter();
  c.increment();
  c.increment();
  c.increment();
  print(c.value);
}

Test yourself

When does setUp run?
- Once after all tests
- Once at program start
- Only on error
- Before each test
Show answer

Before each test — setUp runs before each test.

The setUp block

____(() {
  counter = Counter();
});

Show answer

setUp(() {
  counter = Counter();
});

Fixture parts

setUp

Before test
tearDown

After test
Counter()

Fixture object
value

Tested field

Next lesson: Mock

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